I. Field of the Invention
The present invention relates generally to the processing of iron-bearing ore materials and, particularly, to a process for enriching the usable iron ore content of low-grade, iron-bearing feed materials such as are found in tailings piles and which heretofore have not been commercially usable.
II. Related Art
Throughout northeastern Minnesota and other iron mining regions of the world, there exists extensive stockpiles of commercially unusable, low-grade iron ore including large rocks that were rejected as tailings during the active ore removal mining phase because they lacked sufficient quantities of key mineral ores having sufficient iron content to justify further commercial processing. These significant volumes of low-grade ores typically contain less than 34% iron and may contain high concentrations of unusable forms of iron and silica-bearing or clay materials which has rendered these wastes ore deposits as not fit for further processing into taconite pellets or high-grade ore for producing pig iron.
Specifically, the material contained in these large, non-commercial ore stockpiles contains several mineral forms of iron ores, including magnetite (Fe3O4), hematite (Fe2O3), goethite (FeO.OH), siderite (FeCO3) and limonite (FeO.OH.nH2O). All of these forms would be desirable as a concentrate, with the exception of limonite, which has a high quantity of attached water of hydration as an undesirable factor. Also present is a large amount of gangue material which includes several silts and clay materials, namely, chamosite, stilpnomalanene and kaolin. These small clay particles, also known as slimes, contain silica contaminates that are difficult to remove from the mix due to their strong adhesion properties. The clay particles are very small (<5 microns) and have a propensity to coat particles of iron-bearing materials making the extraction and concentration of those materials very difficult.
It is known to use ultrasonic techniques to dislodge gangue particles from iron ores. Various techniques have been employed and an example of this is found in U.S. Pat. Pub. 2010/0264241 A1, which uses an ultrasonic crusher pipe system to separate gangue from ore in a waterborne slurry. Magnetic separators have also been employed to enrich magnetic ore concentrations in a feed material, as shown in U.S. Pat. No. 5,868,255 to McGaa. Although such techniques have been employed with some degree of success, no practical process has heretofore been developed to economically enrich low-grade ores.
It would present a distinct advantage if an overall complete process could be developed whereby non-commercial low-grade iron-bearing materials of various compositions, presently considered waste material, could be processed into a concentrate containing a much higher percentage of iron that can be cost effectively converted into metallic iron and steel.